Recently it has been determined that significant improvement of speech quality can be obtained in a telecommunication channel by restoring attenuated signal power in a frequency range of interest of approximately 100-400 Hz. This improvement has been realized by adding a fixed "frequency dependent gain (emphasis)" function in the frequency range of interest. One such arrangement is disclosed in U.S. patent application Ser. No. 07/620,997, filed Dec. 3, 1990 now U.S. Pat. No. 5,195,132 issued Mar. 16, 1993 and assigned to the assignee of this patent application.
A problem with using the fixed frequency dependent gain function is that sometimes the frequency dependent gain function being inserted will be too large or too small to compensate for the actual frequency dependent attenuation in the frequency range of interest in the particular telecommunication channel. This is because frequency dependent attenuation will be different for different telecommunication channels in the communication system.
Another problem with the use of a fixed frequency dependent gain function arises when there is more than one occurrence of inserting such a frequency dependent gain function in the particular telecommunication channel. This so-called tandem insertion of fixed frequency dependent gain functions causes far too much frequency dependent gain to be inserted in the channel which, in turn, causes poor speech quality at a receiver.